Root cause, not root reason. You are looking down through many reasons. I fell. I fell because the board broke. The board broken because it was rotten. it was rotten because it was wet for a long time. it was wet because of the hole in the roof. The root cause was the hole in the roof. Imagine the connection between the leaf, the branch, the trunk of a tree, and then the roots - this is why 'Root' is used here. Reason is the explanation for a decision, it wouldn't often work with 'root'. Under the sheets / beneath the sheets - both are valid, there is not much difference. Word & Words. 'He said many kind words about you' is the correct usage, word is just a noun, and is counted. 'You must keep your word' is related to 'I give you my word'. This speaker asserts the following: I have good reputation and I am not prepared to risk my reputation by not honouring my promise. If a person breaks promises, their 'word' is worth nothing. Therefore, 'keeping your word' means keeping the value of 'word' by honouring your promises